Extracurricular for grad school

How crucial is it to have a strong extracurricular background when applying for graduate school at an Ivy or similar university? I'm involved in a few environmental conservation projects and will soon volunteer for a week-long paleontological excavation project led by my university and the city Museum, but I'm not sure these sorts of things are significant enough? What activities/projects/volunteer work should I be doing to separate my application from the rest?

Also, as I understand it, research experience is of critical importance. How much experience should I have accumulated by the end of my 4th year of undergrad study, and how advanced should the level of research be? Should I have contributed to a few published papers by this point?

I apologize if these questions seem trivial - I'm a student in Australia and possess only a rudimentary knowledge of the selection processes in top US schools. Also, if it helps - my BSc degree is in physics, but I intend to pursue a PhD in astrophysics.

Actually, grad schools look into major requirements that relate to ur academic progress which are GRE's, GPA and etc. However, lead's schools may consider other requirments like ur experience background, and activities in selecting. So, I'd say that it depends on what school u apply to.

If your extracurriculars are not directly related to your field of study, grad schools really don't care about them. And you don't want them to think you have a ton of interests outside of your work that will possibly detract from your work - you want them to think you're going to be spending all of your time working for them. And you probably will your first couple of years anyway.

Most people applying to the top grad schools will have significant research experience and at least one publication if not more. Without research experience, you really don't have a shot at a top school - GPA, GRE scores, and letters of recommendation are important, but they want to see that you've taken initiative, made sure this is really what you want to do and that you're capable of research, and letters of recommendation from research advisers are always valuable.

Don't just look at the top schools - there's a direct correlation between how many students a program graduates and it's ranking. There are many top researchers in certain fields at smaller schools with lower rankings, and they're still great programs. They're just smaller - easier to make yourself stand out.

I would agree with what the others here have said. Grad schools don't give a rip about extracurriculars. They care about your GPA, your physics GRE, and your undergrad research (which they typically evaluate via letters of recommendation). Consider this from their perspective: they're paying you to go to school, and they want to make sure that you'll succeed in the classes, pass their qualifier, and do good research to earn your PhD. If you fail out, their money is lost on you. This is important to think about when you're filling out applications, because you want to demonstrate to them that you'll graduate from their department. I would emphasize your physics research experience, as well as any courses you've taken (e.g. graduate quantum) which make you especially prepared for grad school.

Having said all that, if you have any extracurricular experience that relates specifically to physics teaching or research, it may help, though not as much as grades, physics GRE, and reserach. For example, if you are looking to do astrophysics, and you've worked at a national lab or observatory, I would mention this. Or if you have teaching experience, you should mention this too. One of my friends from my year taught high school physics for a year before joining our department. I'm sure this played some small role in his acceptance.